The invention relates to a device for setting the gap dimension for a turbomachine, in particular for a gas turbine, with a multiplicity of moving blades arranged in at least one moving-blade row of a rotor arrangement, with a guide-vane carrier surrounding the rotor arrangement and also a turbine casing surrounding the guide-vane carrier, with a multiplicity of heat accumulation segments which are arranged on the guide-vane carrier of the rotor arrangement and at least opposite the moving-blade tips and, together with the moving-blade tips, enclose a gap, and also with at least one drive means which projects radially through the turbine casing and the guide-vane carrier and is operatively connected kinematically to at least one heat accumulation segment and which, when actuated, brings about a radial spacing of the heat accumulation segment.
Turbomachines of the abovementioned type serve primarily either for the controlled compression of gases, as is the case in compressor stages, known as compressors in turbo plants, or for the controlled expansion of highly compressed and fast-flowing media for the drive of gas turbines which are used in a way known per se for energy recuperation. In order to make energy recuperation by means of gas turbine plants as efficient as possible, a declared aim of efforts toward optimization is to increase the efficiency of turbomachines of this type. Attempts are made, by a series of technical measures, to counteract loss mechanisms which occur both when compressing the working media to be compressed and when driving of turbines.
In this connection, it is expedient, in particular, to keep the radial gaps forming in thermal turbomachines between the rotating and the stationary plant components as small as possible, in order to keep as low as possible the loss streams which pass through these gaps and constitute small, but still existing part mass streams of the working medium passing through the turbomachine, without at the same time participating in the desired energy conversion. Loss streams thus constitute loss mechanisms which may considerably reduce the efficiency of turbomachines. Moreover, the hot loss streams lead to heating or overheating of the blade tips. If attempts are made to keep the gaps small, with the result that the loss streams and therefore the heating of the blade tips also remain low, cooling measures are possible more easily or at a lower outlay.
The particular problem with regard to the reduction of loss streams is, on the one hand, the need for a discrete spacing between the stationary and rotating components of a turbomachine, in order to ensure the free running of the rotor arrangement; on the other hand, it is expedient, for the reasons mentioned, to keep this very interspace as small as possible, this being made more difficult by the fact that the plant components of the turbomachine expand under thermal and mechanical load, with the result that the relative positions of the individual components change during the operation of a turbomachine on account of different thermal expansion behaviors. This makes it difficult, moreover, to have as minimal a gap dimensioning as possible for the entire operating range of a turbomachine which, depending on the type of turbomachine, is exposed to a wide temperature spectrum. Thus, because of the centrifugal forces acting on the rotating components and their natural heating, they are subject to more rapid expansion, which would lead, in principle, to a gap reduction, than the complex thermally insulated components of the stator which experience slower heating and, in a thermally stationary operating state, contribute by expansion to an enlargement of the gap dimension. It is expedient, however, to keep this gap dimension as small as possible during operation.
Both active and passive measures are known for monitoring or influencing the gap dimension, passive precautions superficially seeming to be more advantageous, especially since active control precautions implemented by mechanical setting systems for gap control have high complexity and are suitable only to a limited extent for robust machines subjected to high thermal load, such as, for example, gas turbine plants.
One possibility for implementing gap control passively is the specific optimization of material combinations having specifically selected coefficients of thermal expansion, which brings about thermal expansion in all the plant components determining the gap, with the result that, on the one hand, the gap assumes a minimum size and, on the other hand, this minimum gap width is maintained over the entire operating range, that is to say temperature range, of the turbomachines.
Due to the highly complex configuration of known turbomachines, the possibilities for any desired choice of material combinations for stator and rotor components in order to improve the thermal behavior are very limited. Although the choice of material can be made, while taking into account the problem of the gap width, it has nevertheless not been possible hitherto to solve satisfactorily the problem of reducing the gap dimension merely by the choice of the material combination alone.
Another possibility for keeping the gap dimension small is to take into account abrasive surface actions on stator and rotor components. In this case, the surfaces located opposite one another and almost in contact are provided at least partially with abrasive surface coatings which, when the turbomachine is in operation, are stripped away in a controlled manner by being intentionally ground off or down and which thus result in an optimized gap.
However, after only one operating cycle of the turbomachine, the gap forming as a result of abrasive action has an optimized maximum gap width, but one which cannot be reduced again.
Finally, structural measures for a uniform expansion of the rotor and stator components of a turbomachine are also possible, but, overall, entail a considerable extra outlay in structural terms and, moreover, are not suitable for robust use with long-time stability in gas turbines.
Thus, a device for setting the gap between turbine blades and a heat accumulation segment may be gathered from U.S. Pat. No. 5,228,828. The following statements refer to the exemplary embodiment illustrated in FIG. 1 of the US publication. A heat accumulation segment 18, 82 is arranged opposite the individual turbine blade tips 14, 16. The two components enclose a gap. Through the turbine casing wall 36 projects a rotary shaft 12 which is connected to a control cam 44 within the turbine casing. The control cam 44 spaces the flanks 48 and 54 from one another, especially since the components 46 and 52 are clamped together by means of the spring 76. The components 46 and 52 then engage, on the other hand, into corresponding extensions 84 and 86 of the heat accumulation segment 18, in such a way that, in the event of a relative movement of the two components 46 and 52, the heat accumulation segment 18 moves radially away from the turbine blade tips 14 and 16 or toward these. A relative movement of the two components 46 and 52 may be carried out by means of a rotation of the rotary shaft 12 and of the control cam 44 connected to the latter.
The illustration of this known device clearly shows a complicated construction involving a high outlay, with the result that the operation of the gas turbine becomes more susceptible to repair and maintenance.
The object on which the invention is based is to develop a device for setting the gap dimension for a turbomachine, in particular a gas turbine with a multiplicity of moving blades arranged in at least one moving-blade row of a rotor arrangement, with a guide-vane carrier surrounding the rotor arrangement and also a turbine casing surrounding the guide-vane carrier, with a multiplicity of heat accumulation segments which are arranged on the guide-vane carrier of the rotor arrangement and at least opposite the moving-blade tips and which, together with the moving-blade tips, enclose a gap, and with at least one drive means which projects radially through the turbine casing and the guide-vane carrier and is operatively connected kinematically to at least one heat accumulation segment and which, when actuated, causes a radial spacing of the heat accumulation segment, in such a way that, irrespective of the operating state of the turbomachine, the gap has as small a gap width as possible, which can be actively regulated, but at the same time does not require a complicated construction. The mechanical structural measures to be taken in this case are to be implemented simply and cost-effectively and are to satisfy the requirements of robust use with long-term stability, for example in a gas turbine which is in stationary operation.
The solution for achieving the object on which the invention is based is specified in claim 1. Features advantageously developing the idea of the invention are the subject matter of the subclaims and may be gathered from the description and the figures in order to explain exemplary embodiments.
The device according to the invention, as featured in the preamble of claim 1, is designed in that the heat accumulation segment has, in the flow direction of the turbomachine, a conical contour facing the rotor arrangement and is arranged so as to be displaceable parallel to the flow direction, and in that the drive means is connected to the heat accumulation segment directly or via an eccentric unit, in such a way that, when the drive means is actuated, the heat accumulation segment is displaced, with the result that a radial spacing between the heat accumulation segment and the moving-blade tips can be set.
The conical contour of the heat accumulation segment is formed preferably either by a cone envelope or by any by any desired generating curves widening in the flow direction.
The principle on which is based the adjusting mechanism according to the invention for a specific setting of the gap dimension is based on the fact that the gap space enclosed between the moving-blade tips and the heat accumulation segment designed conically in the flow direction is oriented obliquely to the flow direction or to the axial extent of the turbine casing, especially since the moving-blade end edges located at the moving-blade tips are oriented at an inclination to the axis of the rotor arrangement. When, then, a heat accumulation segment, of which the surface facing the rotor arrangement runs approximately parallel to the moving-blade end edges, is arranged on the guide-vane carrier so as to be spaced in this way, it is sufficient merely to obtain the axial displacement of the heat accumulation segment in order to change the actual radial clearance between the heat accumulation segment and the moving-blade end edge.
As simple a construction as possible of the device according to the invention for setting the gap dimension is implemented, in particular, by a simple and direct kinematic coupling of a drive means to the heat accumulation segment. Alternative solutions for a kinematic coupling of this type are described with reference to the exemplary embodiments described in more detail below. The drive means ensures, in particular, the axial displaceability of the heat accumulation segment, with the result that the radial clearance between the heat accumulation segment and the moving-blade tip can be set specifically. Preferably, the drive means projecting from the turbine casing is connected to a corresponding drive system which, in turn, is provided with an overload or slipping clutch which ensures that, in the event of contact between the heat accumulation segment and a moving-blade tip, no further axial advance and therefore radial approach between the heat accumulation segment and a moving-blade tip can take place. In particular, the overload unit, designed as an overload clutch, ensures that, in the event of force-induced contact between the heat accumulation segment and at least one moving-blade tip, that position of the heat accumulation segment is maintained in which the heat accumulation segment is just not in contact with the moving-blade tip and a minimum intermediate gap is therefore enclosed between the moving-blade tip and the heat accumulation segment.
In the direction of rotation of the guide-vane tips rotating within the guide-vane carrier, a multiplicity of directly adjacent heat accumulation segments for each moving-blade row are arranged opposite the moving-blade tips. Each individual heat accumulation segment is provided with a device according to the invention for setting the gap dimension, so that a multiplicity of drive means projecting through the turbine casing are provided. In principle, it is possible, by the individual actuation of every single drive means, to adjust every single heat accumulation segment individually in space, but it is also conceivable to couple the drive means for each single heat accumulation segment to one another mechanically and activate them correspondingly via a common adjusting mechanism.